MAC extensions for smart antenna support

ABSTRACT

Apparatus and methods implement aggregation frames and allocation frames. The aggregation frames include a plurality of MSDUs or fragments thereof aggregated or otherwise combined together. An aggregation frame makes more efficient use of the wireless communication resources. The allocation frame defines a plurality of time intervals. The allocation frame specifies a pair of stations that are permitted to communicate with each other during each time interval as well as the antenna configuration to be used for the communication. This permits stations to know ahead of time when they are to communicate, with which other stations and the antenna configuration that should be used. A buffered traffic field can also be added to the frames to specify how much data remains to be transmitted following the current frame. This enables network traffic to be scheduled more effectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.10/188,188, filed Jul. 2, 2002, is now U.S Pat. No. 7,360,403 B2;

Which was a non-provisional application claiming priority to provisionalapplication Ser. No. 60/363,030, filed on Mar. 8, 2002, entitled “MACExtensions For Smart Antenna Support,” the teachings of which areincorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to wireless communications. Moreparticularly, the invention relates to medium access control (MAC)frames and mechanisms enabling smart antenna use, improving channelutilization, and increasing communications throughput.

2. Background Information

Initially, computers were most typically used in a standalone manner. Itis now commonplace for computers and other types of electronic devicesto communicate with each other over networks. The ability for computersto communicate with one another has lead to the creation of smallnetworks comprising two or three computers to vast networks comprisinghundreds or even thousands of computers. Networks can be set up toprovide a wide assortment of capabilities. For example, networkedcomputers can be established to permit each computer to share acentralized mass storage device or printer. Further, networks enableelectronic mail and numerous other types of services. Networks have beenestablished in a wired configuration in which each entity on the networkhas a direct physical electrical connection to the network. Morerecently, advances in wireless technology has made it possible fornetwork devices to communicate with others via radio frequency (RF) orother types of wireless media.

To implement a wireless network, each device (computer, access point,etc.) includes one or more antennas through which data is transmitted orreceived. One type of antenna configuration is referred to as singleinput, single output (SISO) and is depicted conceptually in FIG. 1. Twonetwork stations 10 and 12 are shown in communication with each other.The stations could be computers, access points, and the like. In a SISOconfiguration, each station 10 and 12 includes a single antenna 14 and16, respectively. Data is communicated between the stations 10, 12 in anexchange sequence via the single wireless link 18.

An exemplary exchange sequence is illustrated in FIG. 2. One of thestations 10, 12 sends a data frame 20 to the other station whichresponds with an acknowledgment frame 22. The data frame may include apreamble 24, a header 26 and a data payload 28. Similarly, theacknowledgment frame 22 includes a preamble 30, a header 32 and a datapayload 34. The data frame conveys data to the receiving station and theacknowledgment frame lets the sending station know that the data framewas correctly received. If the data frame was not correctly received(e.g., due to noise or interference), the sending station may resend thedata frame.

The total elapsed time required for the data frame 20 and subsequentacknowledgment frame 22 to be transmitted in a SISO antennaconfiguration is shown in FIG. 2 as time T_(SISO). To a certain extent,the information contained in data frame 20 may be transmitted in lesstime using a multiple input, multiple output (MIMO) configuration suchas that shown in FIG. 3. As shown, stations 10, 12 each includes a pairof antennas that communicate with the pair antennas on the otherstation. Thus, for example, antenna 40 can communicate with antenna 44and antenna 42 can communicate with antenna 46, thereby establishing twosimultaneously available communication links 48 and 50 between stations10 and 12. This type of MIMO configuration is referred to as a “2×2”MIMO configuration, and other types of MIMO configurations exist inwhich more than two antennas at each station are implemented such as“3×3” MIMO, etc.

The advantage of a MIMO antenna configuration is illustrated with regardto FIGS. 4 a-4 c. FIG. 4 a simply repeats the SISO frame exchangesequence from FIG. 2. As noted above, the time required to transfer thedata and acknowledgment frames is T_(SISO). FIGS. 4 b and 4 c depict theframe exchange sequence using the 2×2 MIMO antenna configuration of FIG.3. With MIMO, the bit stream can be broken into two parts and the partscan then be transmitted simultaneously via the two communication links48 and 50. Thus, the overall time required to transfer the sameinformation is advantageously reduced. In FIG. 4 c, the total time isshown as T_(MIMO), which is less than T_(SISO). The time savings largelycomes from being able to divide the data payload 28 of the data frame 24into two smaller fields 52 and 54. Various techniques are known fordoing this such as putting all of the even bits of data field 28 intofield 52 and the odd bits into field 54. At the receiving station, thedata parts 52 and 54 then can be reassembled into a single data payload.

Although the data field 28 advantageously can be broken apart forconcurrent transmission, not all of the fields in the frames can bebroken apart. Specifically, the preamble and header fields 24 and 26must be maintained in their entirety. This is so because those fieldscontain information that is necessary for the proper reception of thedata from the network. Also, the acknowledgment frame, being relativelysmall, is not broken apart. Thus, although 2×2 MIMO provides twoindependent and simultaneous communication links, communicationthroughput speed is not doubled.

The preceding discussion illustrates two problems for which solutionsare highly desirable. One problem concerns how to take advantage of theincreased communication speed provided by a MIMO antenna configuration.As noted above, a 2×2 MIMO configuration makes it possible to transmittwice as many bits in the same amount of time as in a SISOconfiguration. However, the overhead information, much of which cannotbe broken apart, contained in typical wireless communication framesreduces the throughput gains that otherwise would be possible.

Another problem is that it is desirable to provide wireless networksthat can be configured as flexibly as possible. For example, it might bedesired for some stations to be SISO only while other stations arecapable of MIMO communications. Further still, of the MIMO stations, itmight be desirable for some stations to be configured as 2×2 MIMO, whileother MIMO stations are 3×3 MIMO. It might also be desirable for somestations to reconfigure themselves for different types of MIMO or SISOconfigurations during operation as they communicate with other stationson the network. In general, MIMO stations may not know in advance whichantenna configuration should be used to receive an incoming frame fromthe air.

Moreover, any improvement to the efficiency of wireless communicationsis desirable. A system that solves the problems described above and, inother respects, generally improves the efficiency of wireless channelutilization would be highly desirable.

BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The preferred embodiments of the present invention solve the problemsnoted above by providing apparatus and methods for implementing variousnew types of communication frames and mechanisms. Such new frame typesinclude forward frames, aggregation frames, feedback frames, andallocation frames. In general, the forward frame represents a shortenedversion of conventional data frames. Specifically, the headerinformation has been encoded differently to require fewer bits. Theaggregation frames include a plurality of MAC service data units (MSDUs)or fragments thereof aggregated together. An aggregation frame makesmore efficient use of the wireless communication resources by combiningtogether data units that otherwise would have been transmitted inseparate data frames, each frame including its own overhead information.The feedback frame provides acknowledgment to a group of transmittedframes each of which would otherwise require a separate acknowledgementframe. The feedback frame also contains the channel state informationthat may be explored by the transmitting station in coding the MIMO bitstreams to reduce reception errors. The allocation frame defines aplurality of time intervals. The allocation frame specifies a pair ofstations that are permitted to communicate with each other during eachtime interval as well as the antenna configuration to be used for thecommunication. The allocation frame is broadcast to network stationsusing the conventional SISO antenna configuration. This frame enablesstations to know ahead of time when they are to communicate, with whichother stations they are to communicate and the antenna configurationthat should be used. This frame also informs SISO-only stations offorthcoming MIMO transmissions activities on the medium so that theSISO-only stations respect the MIMO transmissions even though they donot understand those transmissions.

In accordance with one preferred embodiment of the invention, a methodof implementing a wireless network having a plurality of wirelessstations comprises first forming an aggregation frame to include aplurality of data unit fields and corresponding length fields. The dataunit fields are used to hold data units and the length fields are usedto hold values indicating the length of corresponding data unit fields.Then the aggregation frame is transmitted to a receiving station fordecoding and recovering the aggregated data units.

In accordance with another preferred embodiment, a method ofimplementing a wireless network having a plurality of wireless stationscomprises forming an allocation frame to specify a plurality of timeintervals. For each time interval, the allocation frame identifies apair of stations to communicate during the time interval and aconfiguration for the antenna communications between the identified pairof stations. This frame is broadcast to the network for decoding by thereceiving stations in the network.

If desired, a buffered traffic field can be added to an aggregationframe, an allocation frame or other types of frame. The buffered trafficfield specifies the amount of data units associated with the sametraffic stream remaining to be transmitted following the transmission ofthe current frame. This field permits network traffic to be scheduledmore effectively.

Also, a forward frame can be provided which communicates data betweenwireless stations. The forward frame preferably includes less headerinformation than conventional data frames. Specifically, the forwardframe includes a direction traffic stream and association identifier(DTAID) field which replaces four address fields. The forward frame'sDTAID field can be used to obtain the needed MAC addresses frompreviously transmitted management frames.

These and other aspects and benefits of the preferred embodiments of thepresent invention will become apparent upon analyzing the drawings,detailed description and claims, which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 shows two wireless devices communicating with each other using asingle input, single output (SISO) antenna configuration;

FIG. 2 shows a timing sequence associated with the SISO configuration;

FIG. 3 shows the wireless devices of FIG. 1 communicating with eachother using a multiple input, multiple output (MIMO) antennaconfiguration;

FIGS. 4 a-4 c show timing sequences associated with the SISO and MIMOantenna configurations of FIGS. 1 and 3;

FIG. 5 shows a system diagram of a pair of wireless stations;

FIG. 6 shows a preferred embodiment of an aggregation frame usable toaggregate multiple data fields and/or fragments of data fields into asingle frame to thereby increase the amount of data being transmittedrelative to the amount of overhead information;

FIG. 7 shows an exemplary wireless network comprising a plurality ofstations and an access point;

FIG. 8 shows an exemplary preferred embodiment of an allocation frameusable to permit stations to know what PHY configuration to use whencommunicating on the network

FIG. 9 conceptually illustrates the use of the allocation frame;

FIG. 10 is a more detailed example of the use of an allocation frame;

FIG. 11 shows an aggregation frame including a buffered traffic field topermit a network coordinator to more efficiently schedule networktraffic;

FIG. 12 shows a preferred embodiment of a forward frame; and

FIG. 13 shows a preferred embodiment of a feedback frame.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, semiconductor companies may refer to a component andsub-components by different names. This document does not intend todistinguish between components that differ in name but not function. Inthe following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”. Also, theterm “couple” or “couples” is intended to mean either a direct orindirect electrical or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directelectrical connection, or through an indirect electrical or wirelessconnection via other devices and connections. The term “frame” refers toa basic communication structure which includes overhead information anddata information. The term “data unit” simply refers to a segment ofdata comprising one or more bits. In the context of the 802.11 standard,a data unit is a MAC service data unit, but the term “data unit” isbroader than just 802.11 wireless networks. To the extent that any termis not specially defined in this specification, the intent is that theterm is to be given its plain and ordinary meaning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedbelow in the context of the 802.11 family of wireless standards. The802.11 standard is formally known as the “ISO/IEC 8802-11 InternationalStandard (ANSI/IEEE Std 802.11)” referred to herein as the “802.11standard” for sake of convenience and incorporated herein by reference.It provides wireless medium access control (MAC) and physical layer(PHY) specifications. The 802.11e/D2.0a draft standard defines, on thebasis of the 802.11 standard, Medium Access Control (MAC) enhancementsfor quality of service (QoS). Referring to FIG. 5, a pair of wirelessdevices (also called “stations”) 100 and 102 are shown comprising awireless network 90. Although only two stations are shown in wirelessnetwork 90, in general the network can include more than two stations.Each station 100, 102 comprises host logic 104 (e.g., notebook computer,handheld computer, PDA, etc.) which communicates with another stationvia a wireless medium 112 using a MAC sublayer 106 and a PHY layer 108.The MAC sublayer 106 provides a variety of functions and services tofacilitate effective wireless communications between stations. Examplesof such services include data frame transmission and reception,security, and others. The host 104 uses these services to effectuatecommunications across the wireless medium 112. The PHY layer 108provides an interface between the MAC layer 106 and the wireless mediumand, as such, couples to one or more antennas 110. MAC and PHY layersare well known in the art and are described in greater detail in the802.11 standard.

The currently adopted 802.11 standard defines a structure for variousframe types such as control frames, data frames, and management frames.The discussion which follows describes the use of the basic 802.11 framestructure to implement various frame type enhancements to address theproblems noted previously. Implementing such features in802.11-compliant devices requires several variations from the currentlyadopted standard. These variations have been implemented in thefollowing discussion and associated figures. It should be understood,however, that the scope of this disclosure and the claims that followneed not be limited to the 802.11 context.

In the context of 802.11, however, data frames are also referred to asMAC protocol data units (MPDUs). An MPDU generally comprises a MACheader, a data portion, and a frame check sequence (FCS) field. The PHYlayer may add on a PHY preamble and a PHY header as described above. Thedata field contains a MAC service data unit (MSDU) or a fragmentthereof. Based on network activity, a station's MAC 106 may beprogrammed to fragment MSDUs in excess of a given length. Each fragmentis transmitted in a separate frame with its own MAC header and FCSinformation as well as its own PHY header and preamble.

In some instances, it may be desirable not to send fragmented data inseparate frames because of rapidly changing network conditions. That is,while network conditions may have been such that fragmentation made themost sense at the time, the conditions may have changed. However,fragments that have already been transmitted and need to beretransmitted due to transmission failures must proceed on with beingsent in separate frames—the current 802.11 standard does not permitotherwise. Further, some MSDUs may be of a length less than the maximumpermissible size of an MSDU in a MPDU. However, the current 802.11standard requires such MSDUs to be placed into separate MPDUs.

In accordance with a preferred embodiment of the invention, the 802.11standard can be extended so as to provide for a new type of frame calledan “aggregation” frame (although the name of the frame type is notsignificant). An aggregation frame permits multiple MSDUs and/ormultiple fragments of the same or different MSDUs to be placed into asingle 802.11 MAC frame. This advantageously increases the amount ofdata being transmitted relative to the associated overhead and preambleinformation.

An exemplary embodiment of an aggregation frame is shown in FIG. 6. Asshown, aggregation frame 120 comports with conventional 802.11 frameprotocol in that it contains a MAC header 116, a frame body 118 and aframe check sequence (FCS) 134. The FCS 134 enables error detection andis implemented in accordance with conventional 802.11 protocol. The MACheader 116 and frame body 118 include information pertinent toaggregating MSDUs or fragments thereof. Some of this information isrelevant to specifying that the frame is an aggregation frame and otherinformation is relevant to specifying how the data is aggregated in theframe body 118. The header 116 preferably includes a frame control field122, a DTAID field 124 (described in detail regarding FIG. 12), a framesubbody count field 126, and a sequence control field 128. The framebody 118 preferably includes one or more subbody length fields 130 andone or more frame subbody fields 132. In general, each subbody field 132contains an MSDU or a fragment of an MSDU. By inclusion of MSDUs orfragments in the subbody fields 132, MSDUs and fragments can be combinedtogether into a single frame for transfer between peer MAC entities.

In accordance with the 802.11 standard, the frame control field 122 is a16 bit field. The frame control field 122 of the aggregation frame 120preferably comprises the bit assignments shown below in Table I.

TABLE I Frame Control of Aggregation Frame Bit(s) Value DesignationDescription 0-1 00 Protocol Version Specifies the current 802.11 std 2-311 Type Specifies the type of frame 4-7 1000 Sub-type Specifiesaggregation frame  8 To DS Specifies whether the frame is destined forthe distribution system (DS)  9 From DS Specifies whether the frame camefrom the distribution system (DS) 10 More Fragment Specifies whetherthere are more fragments that belong to the same MSDU as the datacontained in the last frame subbody field of the Aggregation frame 11Ack Acknowledgment request 12 Power Management Specifies powermanagement mode 13 More Data Specifies whether more MSDUs are bufferedfor the addressed station at an access point (AP) after the transmissionof this frame 14 Wired Equivalent Indicates whether the frame Privacy(WEP) body contains information that has been processed by the WEPalgorithm 15 Forward error correction Enables forward error (FEC)correction

Bits 8-9 and 12-15 are set in accordance with currently adopted 802.11standard. The frame type identified by bits 2 and 3 specify a frame typethat previously had been reserved. The aggregation frame describedherein does not fall within any of the currently specified types, so anew type has been defined. The sub-type field in bits 4-7 are set to avalue of “1000” so as to indicate that the frame type specifically is anaggregation frame. The sub-type value of “1000” can be varied asdesired. The More Fragment bit 10 preferably is set to a value of 0 toindicate that the frame contains the sole or final fragment of an MSDUin the last frame subbody field and to 1 to indicate that the framecontains a non-final fragment of an MSDU in the last frame subbodyfield. Acknowledgment bit 10 preferably specifies whether or not theaggregation frame is to be acknowledged (at the MAC level). The framecontrol field 122 thus generally specifies that the frame comprises anaggregation frame and other control information.

Referring still to FIG. 6, the DTAID field 124 preferably specifies thetraffic stream to which the data contained in the frame subbodiesbelongs. The MAC sublayer 106 can accommodate uniquely identifiablemultiple traffic streams between pairs of stations. The frame subbodycount field 126 indicates the number of frame subbodies 132 contained inthe frame 120. Each subbody 132 has an associated sequence control field128 and a subbody length field 130. The sequence control fields 128contain sequence control values for each of the frame subbodies 132. Thesequence control values include the sequence number of the MSDU in acorresponding frame subbody field 132. For example, sequence controlfield 1 contains sequence control information associated with framesubbody 1. In accordance with conventional 802.11 protocol, each MSDU isassigned a unique sequence number to enable a receiving station toprocess the MSDUs in the order in which they were transmitted. Thesequence control field 128 may also include a fragment number. Allfragments comprising an MSDU are assigned the same sequence number butincremental fragment numbers. Thus, if the corresponding frame subbodyfield 132 contains a fragment of an MSDU, rather than a complete MSDU,the fragment number in the sequence control field 128 includes thecorrect fragment number. If the corresponding subbody field 132 containsan entire MSDU, the fragment number preferably is set to 0.

In addition to a sequence control field 128, each frame subbody 132preferably also has associated with it a subbody length field 130. Eachsubbody length field specifies the length of the associated MSDU, orfragment thereof, contained in the corresponding subbody 132. The lengthpreferably is specified in units of “octets” (8 bits), but other lengthunits can be used as well.

The aggregation frame 120 includes at least two subbody fields 132. Asexplained above, each subbody field 132 contains an MSDU, or a fragmentthereof, that corresponds to the traffic stream specified by the DTAIDfield 124, plus, as would be understood by those skilled in the art,appropriate encryption overheads (such as ICV and IV) when the WEP bitis set in the frame control field 122. Preferably, but not arequirement, each subbody field 132 is zero padded by one octet if thecorresponding subbody length field 130 is an odd value so thatsuccessive frame subbodies begin on even octet boundaries. Otherfeatures can be implemented if desired. For example, frame subbodies ina given aggregation frame 120 may be either not encrypted at all orencrypted separately but using the same encryption method or algorithm.Further, frame subbodies in a given aggregation frame may either be notFEC encoded at all or FEC encoded separately but using the same code.

In accordance with another preferred embodiment of the invention, a MACframe is encoded so as to allocate time intervals in which pairs ofstations can communicate with each other according to a specifiedantenna configuration. This type of frame is called an “allocation”frame (again, the name designation for the frame itself is not intendedto impart any limitations). The allocation frame advantageously enablesnetwork stations to know ahead of time what antenna configuration theyare to use. Referring to FIG. 7 for context, a wireless networkcomprises a plurality of stations 142-148, designated in FIG. 7 asStation A-Station D, respectively. The network also includes an accesspoint (AP) 140 which provides connectivity to a wire- or/andwireline-linked distribution system. The AP 140 further contains a“coordinator” 149 which preferably performs bandwidth management andscheduling on the wireless medium. The coordinator 149 may be aso-called “hybrid” coordinator currently being proposed for the802.11e/D2.0a draft standard.

One of the functions performed by the coordinator 149 is to generate andtransmit allocation frames to the various stations 142-148. An exemplaryembodiment of an allocation frame is shown in FIG. 8 and discussedbelow. The allocation frame is transmitted by the coordinator 149 to thestations preferably using a SISO antenna configuration so that allstations, even those stations that are not MIMO capable, in the networkcan correctly receive the allocation frame.

Referring now to FIG. 8, a preferred embodiment of an allocation frame150 is shown comprising a frame control field 152, a duration field 154,a BSSID field 156, an allocation count field 158, one or more allocationfields 160 and an FCS field 168. As explained previously, an 802.11frame control field 152 includes bits for a type and a subtype. Tospecify an allocation frame, the type bits 2 and 3 preferably are set tovalues of 1 and 0, respectively, to specify a “control” frame type. Inthe current version of the 802.11 standard, a control subtype field of0010 is reserved. In accordance with the preferred embodiment of theinvention, however, this subtype value (0010) is used to signify anallocation frame subtype.

The duration field 154 preferably is used to encode the duration in, forexample, microseconds, of all of the time intervals specified in theallocation frame. All the stations in the network decode this field andrefrain from transmissions within the duration indicated by this field,unless they are specified to be a transmitting station via the DTAIDsubfield 162 of one of the allocation fields 160 (to be furtherdescribed below). The BSSID 156 preferably is the MAC address of the AP140 containing the active coordinator 149. All the stations in the basicservice set (BSS) containing this AP recognize this address and processthe allocation frame. Further, the allocation count 158 specifies thenumber of time intervals defined by the allocation frame.

Each allocation frame 150 specifies one or more allocation timeintervals. In each interval, a pair of stations are permitted tocommunicate with each other using an antenna configuration specified forthat particular interval. This concept is illustrated in FIG. 9 in whichan allocation frame 150 is shown followed by a series of n timeintervals 155 (interval 1-interval n). The allocation frame 150 definesthe number of time intervals 155 (e.g., n) and other specificconfiguration features of the communications between stations that areto be allowed during each of the time intervals. The duration field 154preferably is set to the sum of all of the intervals 155 allocated bythe allocation frame. All stations, including legacy SISO-only stations,receive the allocation frame and set their NAV (network allocationvector) to the received duration value so that they will not transmitwithin that duration unless otherwise specified to transmit within theduration by the allocation vector. The NAV is a virtual carrier sensemechanism, as opposed to an actual carrier sense mechanism and is alsospecified by the 802.11 standard. This prevents stations that do notphysically sense an actually busy medium to be busy from transmittingduring the intended transmission period.

Referring again to FIG. 8, the allocation fields 160 following theallocation count field 158 include information regarding the specificsof each allocation time interval. Each allocation field 160 preferablyincludes three fields of information, namely, a DTAID subfield 162, aPHY configuration subfield 164 and a time interval subfield 166. Eachtime interval allocates resources for a transmitting station to transmitdata to a receiving station. The DTAID subfield 162 specifies indirectlythe address of the transmitter and the address of the receiver, as theDTAID was linked to those addresses through previously communicatedmanagement frames according to the 802.11e/D2.0a draft standard. The PHYconfiguration subfield 164 preferably specifies the configuration to beused for the transmission and reception within the correspondinginterval. More specifically, the PHY configuration 164 may identify thePHY rate (which, in turn, identifies the modulation and coding schemes)and transmit/receive antenna type (as used for beamswitching,beamsteering, beamforming, transmit diversity, receive diversity,spatial multiplexing, etc.). The time interval subfield 166 preferablyspecifies a time limit for transmission from the transmitter station tothe receiver station as identified in the DTAID subfield 162. The timelimit may be provided in any suitable units such as microseconds.

Referring now to FIG. 10, a series of intervals 172 are shown followingan allocation frame 150. In accordance with a preferred embodiment ofthe allocation frame feature, the first frame 174 in an intervalpreferably begins at a time T from the end of the allocation frame thatallocated that interval, where T equals “aSIFSTime” or simply “SIFS”(known to those of ordinary skill in the art and define in the 802.1astandard as 16 microseconds) plus the sum of all preceding intervalsallocated by the same allocation frame. The first frame 174 in each timeinterval preferably has a full PHY preamble. Each successive frame 176within the same interval starts at preferably aSlotTime from the end ofthe preceding. The 802.1a standard specifies aSlotTime to be 9microseconds. Each such successive frame 176 preferably has a short PHYpreamble as defined in the 802.11 standard.

Once the coordinator 149 broadcasts the allocation frame 150 to thestations in the BSS, the receiving stations decode the allocation frameto determine when they are to transmit and/or receive. In this manner,each station will know ahead of time what antenna configuration (e.g.,SISO, 2×2 MIMO, etc.) to use and when. The stations permitted tocommunicate in any given interval can be whatever stations are desired.Each interval can be set up for a unique pair of stations or,alternatively, more than one time interval defined in an allocationframe can be used for the same pair of stations. Following the end ofall of the time intervals defined by the allocation frame, thecoordinator 149 may issue another allocation frame 150 thereby defininganother set of time intervals.

FIG. 11 shows another preferred embodiment of the invention. The frameshown in FIG. 11 is an aggregation frame 120, as described previously.All of the fields shown in the frame 120 in FIG. 11 are the same as thatdescribed above with the exception of the “buffered traffic” field 180.This field can be inserted into other frame types besides the allocationframe. The buffered traffic field 180 preferably specifies or otherwiseindicates to a coordinator, such as coordinator 149 in FIG. 7, how muchdata associated with the traffic stream specified by the DTAID field 124remains after the current frame or how much time is needed in sendingthat remaining data. Such remaining data is buffered at the transmittingstation and is awaiting transmission over the wireless network. Thisinformation is useful for scheduling subsequent communications acrossthe wireless network.

The buffered traffic field 180 preferably comprises a 16-bit field. Bit15 is used to encode a “Unit” subfield and bits 14-0 are used to encodea traffic stream state. In accordance with a preferred embodiment of theinvention, if the Unit subfield is set to a 0, the traffic stream statein bits 14-0 indicates a time amount, preferably in units of 8microseconds, needed for transmitting the buffered data present at thetransmitting station belonging to the traffic stream specified by theDTAID field 124. Alternatively, when the Unit subfield is set to a 1,the traffic stream state in bits 14-0 indicate the remaining trafficamount in units of, for example, 64 octets.

In accordance with another preferred embodiment of the inventionresulting in increased efficiency in a wireless network, the 802.11 MACstandard can be extended to provide for a “forward” frame. A forwardframe is generally a shortened version of a standard MAC data frame. Astandard 802.11 data frame includes four address fields requiring 6octets each, 24 octets total. The addresses in these fields depends onthe types of data frame. For example, the four address fields mayinclude a receiver address, a transmitter address, a destinationaddress, and a source address. A forward frame eliminates the need forthat much address information.

Referring now to FIG. 12, an exemplary embodiment of a forward frame 200is shown comprising a frame control field 202, a DTAID field 204, asequence control field 206, a frame body 208 and a FCS field 210. Theframe control field 202 identifies the frame as a forward frame by theway its type and subtype subfields are encoded (11 and 0000,respectively). The sequence control, frame body and FCS fields areencoded as described previously.

In accordance with the preferred embodiment, a two octet DTAID field 204replaces the 24 octet address fields of conventional 802.11 data frames.The DTAID field includes a direction (D) bit concatenated to a TAIDfield. The TAID field includes a traffic stream identifier (TID) and anassociation identifier, as defined in the 802.11e/D2.0a draft standard.Preferably, a previously transmitted management frame also includes amatching TAID field. Such a management frame also includes a sourceaddress and a destination address associated with the TAID information.One or more of the network stations receive the management frame andstore the source and destination addresses and associated TAIDinformation. With that routing information disseminated throughout thenetwork, each subsequent data frame does not necessarily need all fouraddress fields. Any needed MAC addresses can be looked up from suchpreviously transmitted management frames. The direction bit may beencoded as a “0” to indicate a frame from a coordinator to a station ora “1” to indicate a frame from a station to the coordinator or anotherstation.

FIG. 13 shows a preferred embodiment of a feedback frame 220. This frameincludes a frame control 222, DTAID 224, buffer size 226, sequencenumber 228, acknowledgment (ACK) bitmap 230, channel state 232 and FCS234. The frame control 222, DTAID 224, sequence number 228 and FCS 234are as described above with the type and subtype fields in the framecontrol encoded to specify a feedback frame. The buffer size and ACKbitmap fields 226, 230 are used for group frame transmissions andcorresponding group acknowledgments and are described in detail incopending application entitled “A Method and System for GroupTransmission and Acknowledgment,” incorporated herein by reference. Inshort, the feedback frame may provide acknowledgment information for agroup of previously transmitted frames. The channel state field 232indicates channel state information (CSI). CSI generally includesinformation on the channel used in transmitting the data on the trafficstream specified by the DTAID. Accordingly, the feedback frame providesboth group acknowledgment and channel state information.

The aforementioned features describe various enhancements to currentwireless MAC protocols to accommodate new PHY setups, including newantenna configurations, to increase channel utilization, and hence toimprove user throughput. The above discussion is meant to beillustrative of the principles and various embodiments of the presentinvention. Numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

1. A process of wireless data transmission in a basic service set oftransmitters and receivers, comprising: A. forming a medium accesscontrol allocation frame in a coordinator, the forming including: i.forming a frame control field, a duration field, a basic service setfield, an allocation count field, at least one allocation field, and aframe check sum field; ii. arranging the frame control field to specifyan allocation frame; iii. arranging the at least one allocation field tospecify an active transmitter and receiver of the basic service set, tospecify a physical configuration of the specified transmitter andreceiver, and to specify a time limit for transmission from thespecified transmitter to the receiver; iv. arranging the duration fieldto specify a sum of the time limits of the allocation field; v.arranging the basic service set identification field to contain a mediumaccess control address of a coordinator of the basic service set; vi.arranging the allocation count field to contain the number of allocationfields; and vii. arranging the frame check sum field for all of thefields of the frame; B. transmitting the allocation frame from thecoordinator using only a single input single output antenna; and C.receiving the allocation frame in all the receivers in the basic serviceset, the receiving including each receiver using only a single inputsingle output antenna.
 2. The process of claim 1 in which thetransmitting includes transmitting from an access point that includesthe coordinator.
 3. The process of claim 1 in which the forming a frameincludes forming allocation fields, and arranging each allocation fieldto specify an active transmitter and receiver of the basic service set,to specify a physical configuration of the specified transmitter andreceiver, and to specify a time limit for transmission from thespecified transmitter to the receiver.
 4. The process of claim 1including the active transmitter and receiver communicating with oneanother using the specified physical configuration for the specifiedtime limit.
 5. The process of claim 1 in which arranging the at leastone allocation field to specify a physical configuration of thespecified transmitter and receiver includes identifying modulation andcoding schemes, and transmit/receive antenna type, includingbeamswitching, beamsteering, beamforming, transmit diversity, receivediversity, and spatial multiplexing.